Plane light source device and display device provided with the same

ABSTRACT

The present invention aims to provide a plane light source device having enhanced efficiency of use of light and high brightness uniformity. A plane light source device of the present invention is provided with a housing having an opening section, a scattering plate arranged at the opening section for scattering incoming light and a light source arranged at one side face in the housing, wherein a regular reflection section for regularly reflecting light incoming from the light source is provided in the vicinity of the light source at the bottom surface of the housing that is opposite to the scattering plate and a scatter reflection section for irregularly reflecting light incoming from the light source is provided so as to be adjacent to the regular reflection section.

BACKGROUND OF THE INVENTION

The present invention relates to a plane light source device and adisplay device provided with the same, more particularly to a planelight source device used for a backlight of a display device such as atransmissive-type liquid crystal or the like, and to a display deviceusing this plane light source device.

Japanese Unexamined Patent Publication No. 258764/2002 discloses oneexample of a conventional plane light source device. As shown in FIG. 1,this plane light source device reflects light emitted from alight-emitting diode 2 toward light distribution means 1 having a lightscattering function with reflection means 3 that is arranged to beinclined, and the reflected light is scattered at the light distributionmeans 1, thereby forming surface-like illumination light.

The plane light source device disclosed in Japanese Unexamined PatentPublication No. 258764/2002 uniformly reflects light from thelight-emitting diode 2, arranged at the edge section, toward the lightdistribution means 1 by the reflection means 3, so that the illuminationlight has high brightness in the vicinity of the light-emitting diode 2but has reduced brightness as it is away from the light-emitting diode2, thus being non-uniform. When the illumination light of the planelight source device is non-uniform as described above, the displayedimage has non-uniform brightness or non-uniform chromaticity, therebyentailing a problem of deteriorating an image quality.

SUMMARY OF THE INVENTION

The object of the present invention is to solve the above-mentionedproblem, and to provide a plane light source device having highefficiency of use of light and enhanced brightness uniformity. Further,the object of the present invention aims to provide a plane light sourcedevice capable of obtaining desired brightness distribution dependingupon a characteristic of a display device.

A plane light source device of the present invention includes a housinghaving an opening section, a scattering plate arranged at said openingsection for scattering incoming light, and a light source arranged insaid housing, said plane light source device further including: aregular reflection section which regularly reflects incoming light fromsaid light source and a scatter reflection section which irregularlyreflects said incoming light, wherein both said regular reflectionsection and scatter reflection section are provided at said bottomsurface of said housing opposite to said scattering plate, wherein arefracting device for refracting light emitted from said light sourcetoward said regular reflection section and said scatter reflectionsection is provided at the position where light from said light sourceis emitted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing one embodiment of a planelight source device according to the present invention;

FIG. 2 is a sectional view showing one embodiment of the plane lightsource device according to the present invention;

FIG. 3 is a sectional view showing one embodiment of the plane lightsource device according to the present invention;

FIG. 4 is a sectional view showing one embodiment of the plane lightsource device according to the present invention;

FIG. 5 is a sectional view showing one embodiment of the plane lightsource device according to the present invention;

FIG. 6 is a sectional view showing one embodiment of the plane lightsource device according to the present invention;

FIG. 7 is a sectional view showing one embodiment of the plane lightsource device according to the present invention;

FIG. 8 is a sectional view showing one embodiment of the plane lightsource device according to the present invention;

FIG. 9 is a sectional view showing one embodiment of the plane lightsource device according to the present invention;

FIG. 10 is a sectional view showing one embodiment of the plane lightsource device according to the present invention;

FIG. 11 is a sectional view showing one embodiment of the plane lightsource device according to the present invention;

FIG. 12 is a sectional view showing one embodiment of the plane lightsource device according to the present invention;

FIG. 13 is a sectional view showing one embodiment of the plane lightsource device according to the present invention;

FIG. 14 is a sectional view showing one embodiment of the plane lightsource device according to the present invention;

FIG. 15 is a partial plan view showing one embodiment of the plane lightsource device according to the present invention;

FIG. 16 is a partial plan view showing one embodiment of the plane lightsource device according to the present invention;

FIG. 17 is a partial plan view showing one embodiment of the plane lightsource device according to the present invention; and

FIG. 18 is a partial plan view showing one embodiment of the plane lightsource device according to the present invention.

DETAILED DESCRIPTION

Embodiments of plane light source device according to the presentinvention will be explained with reference to drawings. In each figure,members given same numerals substantially represent the same components.

Embodiment 1

FIG. 1 is a perspective view showing a schematic construction of adisplay device, according to one embodiment, provided with a plane lightsource device 10 of the present invention, and FIG. 2 is a partialsectional view taken along a line A-A of the plane light source deviceshown in FIG. 1. In FIGS. 1 and 2, numeral 3 denotes a housing having anopening section 3 a. A scattering plate 4 that scatters incoming lightis arranged at the opening section 3 a of the housing 3. Numeral 1denotes a line light source that is arranged at one side face 3 c at theinside of the housing 3. Numeral 2 denotes a reflection plate thatreflects incoming light from the line light source 1 toward thescattering plate 4. The reflection plate 2 is composed of a scatterreflection plate 2 a that irregularly reflects the incoming light and aregular reflection plate 2 b that regularly reflects the incoming light,and is arranged at the bottom surface 3 b opposite to the openingsection 3 a of the housing 3. Further, the regular reflection plate 2 bis arranged in the vicinity of the line light source 1, while thescatter reflection plate 2 a is arranged at a position apart from theline light source 1. Numeral 5 denotes a reflector disposed in thevicinity of the line light source 1 for reflecting light, among lightsemitted from the line light source 1, that directs toward the inner wallof the housing 3 toward the reflection plate 2 or the scattering plate4.

As shown in FIG. 1, a liquid crystal display panel 11 or the like as adisplay device is arranged at the light-emitting surface of the planelight source device 10 having the aforesaid construction. Light from theplane light source device 10 reaching the liquid crystal panel 11 ismodulated with an image signal to thereby display each color of R, G andB.

As shown in FIGS. 1 and 2, the scatter reflection plate 2 a is arrangedat the position apart from the line light source 1, while the regularreflection plate 2 b is arranged in the vicinity of the line lightsource 1. The scatter reflection plate 2 a irregularly reflects lightincoming from the line light source 1, while the regular reflectionplate 2 b regularly reflects the incoming light from the line lightsource 1, i.e., reflects the incoming light at an emitting angle equalto the incident angle. Further, an overlapping section is formed at thearea where the scatter reflection plate 2 a and the regular reflectionplate 2 b are adjacent to each other, so as not form a space betweenthem.

FIG. 4 is a view of an optical path for explaining an action of each ofthe scatter reflection plate 2 a and the regular reflection plate 2 bshown in FIGS. 1 and 2.

Light emitted from the line light source 1 is directly incoming orreflected by the reflector 5 to be incoming on the scattering plate 4,scatter reflection plate 2 a or regular reflection plate 2 b. The lightL2 incoming on the regular reflection plate 2 b arranged in the vicinityof the line light source 1 is reflected at an angle equal to theincident angle to be impinged on the scattering plate 4. On the otherhand, the light L1 incoming on the scatter reflection plate 2 a isirregularly reflected in the vicinity of the incoming position tothereby irradiate the scattering plate 4. As shown in FIG. 4, theincident angle of the light incoming on the reflection plate 2 becomesapproximately parallel as it is apart from the line light source 1. Incase where only the regular reflection means is used as the reflectionplate 2, the light whose incident angle is approximately parallel isreflected toward the inner wall of the housing 3, not toward thescattering plate 4, as shown by L11 in FIG. 4, so that the brightness ofthe illumination light is reduced as it is apart from the line lightsource 1. In the present invention, the scatter reflection plate 2 a isarranged at the position apart from the line light source 1, whereby thelight reflected toward the inner wall of the housing 3 can be irradiatedto the scattering plate 4. This can enhance the efficiency of use oflight, thereby being capable of obtaining uniform illumination light atthe scattering plate 4.

As described above, the plane light source device according to thepresent invention has the regular reflection plate 2 b in the vicinityof the line light source 1 and the scatter reflection plate 2 a at theposition apart from the line light source 1. Therefore, light incomingwith an approximately parallel angle at the position apart from the linelight source 1 is reflected by the scatter reflection plate 2 a towardthe scattering plate 4 in the vicinity of the incoming position, therebybeing capable of obtaining uniform illumination light.

Setting the reflectivity of the scatter reflection plate 2 a, regularreflection plate 2 b and reflector 5 to be not less than 90% (preferablynot less than 95%) enables to restrain the reflection loss at thereflection surface. The regular reflection plate 2 b is made of a metalplate such as an aluminum or silver or made by vapor-depositing analuminum or silver on a resinous sheet. The scatter reflection plate 2 ais made by roughening the surface of the regular reflection plate,providing on the surface of the regular reflection plate a scatteringsheet having a function of transmitting and scattering light or made ofa white resinous sheet or made of a metal sheet such as an aluminum orresinous sheet having a white resinous sheet attached thereon or havinga white coating applied thereon.

Usable members for the scattering plate 4 include a resinous plate suchas polyethylene terephthalate (PET), acrylic resin (PMMA) orpolycarbonate (PC) or an optical member such as a glass substrate.

A kind of optical sheet not shown may be provided between the scatteringplate 4 and the liquid crystal display panel 11. Usable kinds of opticalsheet include a scattering sheet, prism sheet or polarizing reflectionsheet, that can control the light distribution characteristic of theemitted light. Further, using the optical sheet such as the prism sheethaving a continuous triangle pole with a vertical angle of approximately90 degrees formed at the side of the display side or the polarizingreflection sheet having a function of reflecting a part of light towardthe side of the scattering plate 4 can further reduce non-uniformbrightness by the light scattering effect by the scattering plate 4 orre-reflection by the reflection plate 2, thus preferable.

Moreover, coating the inside of the housing 3 with a reflection materialor white paint can reduce loss of light emitted from the line lightsource 1.

The reflector 5 is made of a metal plate having a reflection layer madeof a silver or aluminum or made of a white resinous sheet.

Although the above-mentioned plane light source device uses the linelight source 1 as a light source, a plurality of point light sources 1 csuch as LED (Light Emitting Diode) or the like are arranged to form alight source section as shown in FIG. 3. The point light source 1 c iscomposed of an LED chip 13, a heat transferring plate 15 that transmitsheat generated from the LED chip 13, a lens 14 that protects the LEDchip 13 and adjusts the light distribution characteristic of the LEDchip 13, an electrode 16 and a substrate 12 as shown in FIG. 3.

Arranged at the position where light from the point light source 1 c isemitted is a refracting device 6 having a trapezoid sectional shape. Therefracting device 6 refracts light from the light source toward thereflection plate 2. Combining the point light source 1 c having lightdirectivity and the refracting device 6 enables to make lightefficiently reach the reflection plate 2, thereby enhancingcontrollability of the brightness distribution achieved by using thescatter reflection plate 2 a and the regular reflection plate 2 b forthe reflection plate 2.

The point light source 1 c may use a single-colored LED such as R, G, Bor the like in addition to the white LED. The advantage of using theRGB-LED, compared to the white LED, is that higher luminous efficiency(=light flux amount/applied power) can be obtained by a white color madeby mixing RGB. Further, a display having high color reproducibility canbe realized by making the emission spectrum of RGB approximately equalto the transmission characteristic of a color filter RGB (not shown) ofthe liquid crystal panel.

Although the reflection plate 2 is composed of the regular reflectionplate 2 b and the scatter reflection plate 2 a, it should be noted thatthe reflection plate 2 may be composed of a single plate-like opticalmember having a regular reflection section that regularly reflectsincoming light and a scatter reflection section that irregularlyreflects incoming light, this single plate-like optical member beingarranged on the bottom surface 3 b of the housing 3. Moreover, theregular reflection plate may be arranged all over the bottom surface 3 bof the housing 3 and a scattering sheet may be provided on a part of thesurface of the regular reflection plate, to thereby form the regularreflection section and the scatter reflection section. This constructiondecreases the number of components, thereby being capable of reducing aproblem such as positional displacement of the reflection plate.

Embodiment 2

FIG. 5 is a view showing another embodiment of the plane light sourcedevice according to the present invention. Although the line lightsource 1 such as CCFL (Cold Cathode Fluorescent Lamp) or the like or aplurality of point light sources 1 c are arranged at one side in thehousing 3 in the embodiment 1, two line light sources 1 a and 1 b may bearranged at both sides in the housing 3 so as to oppose to each other asshown in FIG. 5. In this case, a reflection plate 25 is composed ofregular reflection plates 2 b 1 and 2 b 2 and a scatter reflection plate2 a, wherein the regular reflection plates 2 b 1 and 2 b 2 are arrangedrespectively in the vicinity of the line light sources 1 a and 1 b,while the scatter reflection plate 2 a is arranged at the centralportion that is apart from two line light sources 1 a and 1 b. The otherconstructions are the same as those in the embodiment 1.

FIG. 6 is a view of an optical path for explaining an action of theregular reflection plates 2 b 1 and 2 b 2 and the scatter reflectionplate 2 a shown in FIG. 5.

Light emitted from the line light sources 1 a and 1 b is directlyincoming or reflected by the reflector 5 to be incoming on thescattering plate 4, scatter reflection plate 2 a or regular reflectionplates 2 b 1 or 2 b 2. The light L4 incoming on the regular reflectionplates 2 b 1 arranged in the vicinity of the line light source 1 a isreflected at an angle equal to the incident angle to be impinged on thescattering plate 4. On the other hand, the light L3 incoming on thescatter reflection plate 2 a is irregularly reflected in the vicinity ofthe incoming position to thereby irradiate the scattering plate 4. Asexplained in the embodiment 1, the incident angle of the light impingedon the reflection plate 25 becomes approximately parallel at theposition more apart from the line light sources 1 a and 1 b. In theembodiment 2, the scatter reflection plate 2 a is arranged at thecentral portion that is apart from the line light sources 1 a and 1 bfor irregularly reflecting light incoming from a pair of line lightsources 1 toward the central portion of the scattering plate 4, therebybeing capable of increasing brightness of the illumination light at thecentral portion.

As described above, the plane light source device according to theembodiment 2 has regular reflection plates 2 b 1 and 2 b 2 arranged inthe vicinity of two line light sources 1 a and 1 b that are arranged atboth sides in the housing 3 so as to oppose to each other and thescatter reflection plate 2 a arranged at the central portion that isapart from the line light sources 1 a and 1 b, thereby being capable ofobtaining illumination light having an ideal brightness distribution inwhich a brightness at the central portion is high.

Although the explanation is made by using the line light source as alight source, a point light source may be used instead of the line lightsource. Further, the same effect can be obtained by the constructionwherein point light sources 1 c 1 and 1 c 2 are used for a light sourceand refracting devices 6 a and 6 b are arranged, as shown in FIG. 7.

As shown in a partial plan view of FIG. 9, an elliptic scatterreflection plate 2 a may be arranged at the central portion as amodified example of the embodiment 2. This modified example enables toselectively enhance the brightness of the illumination light at thecentral portion.

Further, as shown in a partial plan view of FIG. 8, the scatterreflection plates 2 a 1 and 2 a 2 may be arranged at the portion, otherthan the central portion, where the brightness is intended to beincreased. The shape of the scatter reflection plate is freely set so asto be suitable for the type of the light source to be used or desiredbrightness distribution as described above, resulting in obtaining adesired brightness distribution in the illumination light. Suchadjusting method is effective as means for adjusting the brightnessafter the mounting. The scatter reflection plate arranged at theposition other than the central portion may have reflection propertydifferent from that at the central portion.

Although the reflection plate 25 is composed of the regular reflectionplates 2 b 1 and 2 b 2 and the scatter reflection plate 2 a, it shouldbe noted that the reflection plate 25 may be composed of a singleplate-like optical member having a regular reflection section thatregularly reflects incoming light and a scatter reflection section thatirregularly reflects incoming light, this single plate-like opticalmember being arranged on the bottom surface 3 b of the housing 3.Moreover, the regular reflection plate may be arranged all over thebottom surface 3 b of the housing 3 and a scattering sheet may beprovided on a part of the surface of the regular reflection plate, tothereby form the regular reflection section and the scatter reflectionsection. This construction decreases the number of components, therebybeing capable of reducing a problem such as positional displacement ofthe reflection plate.

Embodiment 3

FIG. 10 is a view showing another embodiment of the plane light sourcedevice according to the present invention. Although the light source isarranged at the side face in the housing 3 in the embodiments 1 and 2, aplurality of line light sources 1 may be arranged at the bottom surface3 b of the housing 3 as shown in FIG. 10. In the plane light sourcedevice in the embodiment 3, a plurality of scatter reflection plates 2 aand regular reflection plates 2 b are alternately arranged so as to beadjacent to each other. Further, the line light sources 1 are arrangedon the regular reflection plates 2 b at a predetermined space. The otherconstructions are the same as those in the embodiment 1.

FIG. 11 is a view of an optical path for explaining an action of thescatter reflection plate 2 a and the regular reflection plate 2 b shownin FIG. 10.

Light L6 emitted from the line light sources 1 is incoming on theregular reflection plate 2 b arranged in the vicinity thereof andreflected at an angle equal to the incident angle to be impinged on thescattering plate 4. On the other hand, the light L5 incoming on thescatter reflection plate 2 a is irregularly reflected in the vicinity ofthe incoming position to thereby irradiate the scattering plate 4. Asexplained in the embodiment 1, the incident angle of the light impingedon the scatter reflection plate 2 a becomes approximately parallel atthe position more apart from the line light sources 1. In the planelight source device in the embodiment 3, the line light sources 1 arerespectively arranged on the regular reflection plates 2 b at apredetermined space and the scatter reflection plates 2 a arealternately arranged so as to be adjacent to the regular reflectionplates 2 b. Therefore, light incoming from the line light sources 1 withan approximately parallel angle is irregularly reflected in the vicinityof the incoming position, thereby being capable of enhancing theefficiency of use of light, and hence, uniform illumination light can beobtained.

As shown in FIG. 13, an inclined face may be provided on the scatterreflection plate 2 a as a modified example of the embodiment 3. Thismodified example allows to increase an amount of light incoming on thescatter reflection plate 2 a, thereby enhancing the scattering effect bythe scatter reflection plate 2 a. As a result, more uniform illuminationlight can be obtained.

The angle of the inclined face can be changed depending upon the type ofthe light source to be used or desired brightness distribution. Further,although the inclined face is provided at the scatter reflection platein this embodiment, any shape such as a projection or round shape may beapplied only for effectively impinging light from the light source onthe scatter reflection plate 2 a.

The same effect can be obtained even by using the point light source 1 cexplained in the embodiment 1 as shown in FIG. 12, other than the linelight source 1.

It should be noted that, instead of the reflector 5 used in theembodiments 1 and 2, a reflection material or white paint may be appliedat the inside of the housing 3. This enables to reduce loss of lightemitted from the light source.

It should be noted that, as shown in FIG. 14, the reflection plate 26may be composed of a single plate-like optical member having a regularreflection section 2 b that regularly reflects incoming light and ascatter reflection section 2 a that irregularly reflects incoming light,this single plate-like optical member being arranged on the bottomsurface 3 b of the housing 3. Moreover, the regular reflection plate maybe arranged all over the bottom surface 3 b of the housing 3 and ascattering sheet may be provided on a part of the surface of the regularreflection plate, to thereby form the regular reflection section and thescatter reflection section. This construction decreases the number ofcomponents, thereby being capable of reducing a problem such aspositional displacement of the reflection plate.

Embodiment 4

The construction shown in the embodiments 1 to 3 wherein the scatterreflection plate and regular reflection plate are alternately linearlyarranged causes a rapid change in the brightness at the boundarysection, that is apt to cause non-uniformness in illumination light. Asa method for not attracting attention to the non-uniformness in theillumination light due to the difference in the reflection property, areflection property adjusting section for changing stepwise a scatterreflectance (a ratio of light that is scattered and reflected toregularly reflected light) may be provided between the scatterreflection plate and the regular reflection plate.

FIG. 15 is a partial plan view showing another embodiment of the planelight source device according to the present invention. The plane lightsource device in this embodiment has an area 21 where the boundary 22between the scatter reflection plate 2 a and the regular reflectionplate 2 b is formed into a waveform. This area 21 functions as areflection property adjusting section. Specifically, providing the area21 reduces stepwise the scatter reflectance of light directing from thescatter reflection plate 2 a toward the regular reflection plate 2 b,with the result that the non-uniform brightness caused by the differencein the reflection property between the scatter reflection plate 2 a andthe regular reflection plate 2 b is not so noticeable, thereby beingcapable of obtaining a smooth brightness distribution. Although theboundary 22 between the scatter reflection plate 2 a and the regularreflection plate 2 b is formed into a linear waveform, it should benoted that it may be formed into a curved line. Moreover, it may beformed into a continuous rectangular or convex/concave shape. The otherconstructions are the same as those in the embodiments 1 to 3.

Further, in case where the scatter reflection plate 2 a is arranged onthe regular reflection plate 2 b, the reflection property adjustingsection 21 may be composed by continuously providing circular holes 23,whose diameter increases toward the regular reflection plate 2 b, at theoverlapping section of the scatter reflection plate 2 a and the regularreflection plate 2 b as shown in FIG. 16. According to this modifiedexample, the scatter reflectance of light is reduced stepwise toward theregular reflection plate 2 b, so that the non-uniformness of theillumination light, that is caused by the difference in the reflectionproperty between the scatter reflection plate 2 a and the regularreflection plate 2 b, is made unnoticeable, thereby being capable ofobtaining illumination light, having a smooth distribution, at thescattering plate 4.

Moreover, in case where the regular reflection plates 2 b are arrangedon the scatter reflection plate 2 a as shown in FIG. 17, circular holes24 whose diameter decreases toward the regular reflection plate 2 b maybe provided at the overlapping section of the regular reflection plate 2b and the scatter reflection plate 2 a.

Further, holes provided at the overlapping section are formed such thatthe holes having the same diameter are provided so as to reduce itsdensity in order to reduce stepwise the scatter reflectance of lighttoward the regular reflection plate 2 b.

Moreover, as shown in FIG. 18, an optical member 2 c having a scatterreflectance that is intermediate between the scatter reflectance of thescatter reflection member 2 a and that of the regular reflection member2 b may be provided between the scatter reflection plate 2 a and theregular reflection plate 2 b.

The plane light source device of the present invention has a regularreflection section that regularly reflects incoming light and a scatterreflection section that irregularly reflects incoming light, those ofwhich being suitably arranged, resulting in that an efficiency of use oflight is enhanced and a desired brightness distribution can be obtainedaccording to a characteristic of a display device.

It is to be understood that the above-described arrangements are onlyillustrative of the application of the principles of the presentinvention. Numerous modifications and alternative arrangements may bedevised by those skilled in the art without departing from the scope ofthe present invention, and the appended claims are intended to coversuch modifications and arrangements.

1. A plane light source device comprising a housing having an openingsection, a scattering plate arranged at said opening section forscattering incoming light, and a light source arranged in said housing,said plane light source device further comprising: a regular reflectionsection which regularly reflects incoming light from said light sourceand a scatter reflection section which irregularly reflects saidincoming light, wherein both said regular reflection section and scatterreflection section are provided at said bottom surface of said housingopposite to said scattering plate, wherein a refracting device forrefracting light emitted from said light source toward said regularreflection section and said scatter reflection section is provided atthe position where light from said light source is emitted.
 2. The planelight source device of claim 1, wherein a reflection property adjustingsection that reduces stepwise the scatter reflectance toward saidregular reflection section is provided between said regular reflectionsection and said scatter reflection section.
 3. A display systemcomprising of a display unit and the plane light source device of claim1, wherein said display unit comprising a display device for modulatinglight incoming from said plane light source device.
 4. A display systemcomprising of a display unit and the plane light source device of claim2, wherein said display unit comprising a display device for modulatinglight incoming from said plane light source device.
 5. The plane lightsource device of claim 1, wherein said regular reflection section andsaid scatter reflection section are respectively composed of a regularreflection plate that regularly reflects incoming light and a scatterreflection plate that irregularly reflects said incoming light.
 6. Aplane light source device according to claim 5, wherein said scatterreflection plate and said regular reflection plate are arranged so as tohave an overlapping section where both plates are overlapped with eachother, wherein in case where said scatter reflection plate is arrangedon said regular reflection plate, holes whose diameter increases towardsaid boundary between said scatter reflection plate and said regularreflection plate are provided at said overlapping section of saidscatter reflection plate, and in case where said regular reflectionplate is arranged on said scatter reflection plate, holes whose diameterdecreases toward said boundary between said scatter reflection plate andsaid regular reflection plate are provided at said overlapping sectionof said regular reflection plate.
 7. The plane light source device ofclaim 1, wherein said regular reflection section and said scatterreflection section provided at said bottom surface of said housing arerespectively composed of a regular reflection plate formed all over thebottom surface of said housing and a scattering sheet arranged inintimate contact with a part of said regular reflection plate at theside of said opening section.
 8. The plane light source device of claim1, wherein said boundary between said regular reflection section andsaid scatter reflection section is formed into a waveform.
 9. The planelight source device of claim 1, wherein a reflection section having ascatter reflectance lower than that of said scatter reflection sectionis provided between said regular reflection section and said scatterreflection section.
 10. The plane light source device of claim 1,wherein an inclined face is provided at said scatter reflection section.11. The plane light source device of claim 2, wherein said regularreflection section and said scatter reflection section are respectivelycomposed of a regular reflection plate that regularly reflects incominglight and a scatter reflection plate that irregularly reflects saidincoming light.
 12. The plane light source device of claim 2, whereinsaid regular reflection section and said scatter reflection sectionprovided at said bottom surface of said housing are respectivelycomposed of a regular reflection plate formed all over the bottomsurface of said housing and a scattering sheet arranged in intimatecontact with a part of said regular reflection plate at the side of saidopening section.
 13. The plane light source device of claim 2, whereinsaid boundary between said regular reflection section and said scatterreflection section is formed into a waveform.
 14. The plane light sourcedevice of claim 2, wherein a reflection section having a scatterreflectance lower than that of said scatter reflection section isprovided between said regular reflection section and said scatterreflection section.
 15. The plane light source device of claim 2,wherein an inclined face is provided at said scatter reflection section.